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A new US study has found that around 20 per cent of peanut allergy sufferers may outgrow their need to avoid numerous foods for fear of a severe or even fatal reaction.

The study, by researchers from Johns Hopkins, is reported in the February issue of the Journal of Allergy and Clinical Immunology.

"In our patient group, roughly 20 per cent outgrew their peanut allergy," says Dr Robert Wood, associate professor of paediatrics at Johns Hopkins and lead investigator of the study.

"Until now, the rules have been that when you diagnose a patient with peanut allergy, you tell them that it is a life-long allergy, with no chance of being outgrown," says Wood. "I recommend from this study that children with peanut allergy be retested on a regular basis, every one or two years."

Adults who have not had any reactions since childhood and who have never been retested should also be re-evaluated, according to Wood, who has peanut allergy himself and whose own retest disappointingly found he is still allergic.

The allergy, which can be triggered by a mere 1/1000 of a peanut, causes the most severe reactions of all food allergies. It affects one percent of the population and is responsible for three or four deaths per year in Australia.

Allergic individuals must avoid a vast number of products that contain peanuts, peanut flour or peanut derivatives, including many biscuits, crackers, chips, cereals, baked goods and Asian foods, as well as making sure that a cooking utensil contaminated with peanut residue or oils is not used to prepare their food.

They are also advised to carry an adrenaline shot with them at all times in case of anaphylaxis, the life-threatening allergic reaction that can constrict airways in the lungs, severely lower blood pressure, and cause swelling of the tongue or throat, literally suffocating victims.

The researchers found that people were more likely to outgrow their peanut problem if they had lower levels of peanut specific IgE, antibodies produced by the immune system that cause allergic reactions. Children who had lost sensitivities to other foods, including milk or egg, were also more likely to outgrow peanut allergy.

'Encouraging' but more studies needed

Dr Ian Glaspole, an expert in Allergy, Asthma and Clinical Immunology at Melbourne's Alfred Hospital said the results supported previous work that showed around 18 per cent of sufferers outgrew their allergy. However, he said, it was not clear how the researchers had defined the group of allergy sufferers in the first place.

"Were these people objectively assessed? Maybe they weren't really allergic to peanuts in the first place." he said. "Around 30 per cent of people who claim to have food intolerance fail to show any clinical signs of it."

Dr Glaspole also questioned the use of IgE or loss of sensitivity to milk and eggs as predictors of people who will outgrow their allergies.

"Most children outgrow their allergies to milk and eggs, and the best tests we have for IgE are only 80% sensitive," he said. "There is a large group of people who have no detectable IgE and are still sensitive to peanuts."

"The results of this study are very encouraging but we need a trial that follows people over time," he said.

Dr Wood next plans to monitor children from their initial diagnosis in an attempt to pinpoint other signs that will indicate which people are more or less likely to outgrow the allergy.